Genotoxicity evaluation of the tricyclic antidepressants amitriptyline and imipramine using human lymphocyte cultures

Two tricyclic antidepressants, amitriptyline and imipramine, were evaluated for their in vitro cytogenetic effects in human lymphocyte cultures. Peripheral blood cultures from three normal healthy donors were set up for 72 hr for each of the drugs. The drugs were added at the start (72-hr exposure), 24 hr (48-hr exposure), and 48 hr (24-hr exposure) after initiation of the cultures. The concentrations evaluated at each exposure time were 50, 250, 1,000, and 10,000 ng/ml for amitriptyline and 25, 500, and 5,000 ng/ml for imipramine. The first two concentrations correspond to the plasma levels of the respective drugs after therapeutic doses. All treatments for a donor were given at the same time. Untreated cultures served as controls for the baseline frequency of the parameters assayed. The parameters assayed were chromosome aberrations, mitotic index, and sister chromatid exchanges (SCEs). Amitriptyline was found to be nongenotoxic at plasma levels by all the parameters assayed. However, frequencies of chromosome aberrations and SCEs were significantly increased at concentrations 4 and 40 times the plasma level (1,000 and 10,000 ng/ml) although the actual increases was small. The mitotic index was not affected at any concentration. Through imipramine showed a significant increase in chromosome damage at the upper plasma level and at concentrations higher than that, SCE frequency was significantly increased only at concentration higher than the plasma level (5,000 ng/ml), the actual increase being small for both these parameters. The mitotic index was not affected at any concentration. These results suggest that amitriptyline may be a slightly safer drug than imipramine from a genetic point of view.